I like 4 shield (don't really need higher for cav if you use elite cav shield or knightly heater), level 3 shield is only for the "heater" shield, but it has a slow speed rating, so I wouldn't recommend using it (compared to 100+ with the 2 i mentioned). I think 7 riding is too much unless you're riding the arabian war horse.
Also 7 WM isn't that good. I'm level 30 with 6 WM and my skills are: 1h - 122/polearms - 115
I don't like having 5 PS either. If you only need 6 riding (for a courser, or 5 maybe) then go 18 or 15 agility.
I think this is the best build I've been able to come up with at level 30 for cav:
Strength: 18
Agility: 18
Hit points: 57
Skills to attributes: 2
Ironflesh: 2
Power Strike: 6
Shield: 4
Athletics: 5
Riding: 6
Horse Archery: 0
Power Draw: 0
Power Throw: 0
Weapon Master: 6